High frequency electron discharge device having a grooved cathode and electrodes therefor



Aug. 1, 1967 J. E. BEGGS 3,334,263? HIGH FREQUENCY ELECTRON DISCHARGE DEVICE HAVING A GROOVED CATHODE AND ELECTRODES THEREFOR 3 Sheets-Sheet-l Filed Nov. 12, 1964 I 5 W W f 6 0 5 w m m fl A 0 S S 1/ e 7 m H J Fig.

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Inventor: James E. Beggs, QAWM His Affomey United States Patent 3,334,263 HIGH FREQUENCY ELECTRON DISCHARGE DE- VICE HAVING A GROOVED CATHODE AND ELECTRODES THEREFOR James E. Beggs, Schenectady, N.Y., assignor to General Electric Company, a corporation of New York Filed Nov. 12, 1964, Ser. No. 410,570

11 Claims. (Cl. 313-348) ABSTRACT OF THE DISCLOSURE The grid electrode of a miniature, high power, high frequency electron tube has a circumferential metal ring across which extend a plurality of relatively massive bars in one direction and fine grid conductors in a transverse direction so that the bars both support and cool the fine grid wires. The cathode has channels or recesses which receive the bars, the major portion of the bars extending considerably below the cathode emitting surface.

This invention relates to high frequency electron discharge devices and methods of manufacture, and particularly to such devices for providing high power output.

In my US. Patent 2,680,824, assigned to the assignee of the present invention, a type of electron discharge device having planar electrodes is described and claimed which device may be miniaturized in structure and conveniently provided with accessible ring-like terminals. These miniaturized discharge devices are useful at high frequencies because their electrodes are small in crosssection and relatively closely spaced, thereby reducing inter-electrode capacitance and electron transit time between electrodes.

One advantageous grid construction for a discharge device of this type consists of a plurality of fine grid conductors disposed between the devices planar anode and cathode. A thin grid composed of fine conductors closely spaced to the cathode would provide high mutual conductance, minimum transit time for electrons between the cathode and grid, minimum transit time for electrons passing through the grid, and an even anode field distribution at the cathode. This ideal is extremely difiicult to realize, however, in high power discharge devices because of the high temperatures to which a grid is subjected near the cathode electrode. Several sources of heat tend to warp and even destroy fine grid conductors near a cathode in a high power discharge device. Sources of heat, although not necessarily equally effective, include 1) heat radiated from the cathode; (2) heat radiated from the anode; (3) electron current intercepted by the grid; (4) RR displacement currents charging the gridcathode capacitance, and (5) RF. displacement currents charging the grid-anode capacitance. At high frequencies, on the order of one gigacycle per second, the magnitude of the displacement currents alone can become so high as to melt very fine grid conduct0rs.. Moreover the overheated grid itself tends to emit electrons excessively.

In order to solve the foregoing problems and at the same time attain advantages of a fine conductor grid spaced closely adjacent a cathode, it has been proposed to utilize heavier grid conductors for stiffening a fine conductor grid, for diverting heat or current from the fine grid conductors. For example, it has been proposed that a wire grid be attached to heavy conductor members, which members are located between the grid and the anode, with the fine grid wires therefore being located immediately adjacent the cathode surface. Because of the bulk of heavy support members or conductors, this construction involves either an increased grid-anode spacing with an unacceptable transit time, or alternatively, an in- 3,334,263 Patented Aug. 1, 1967 creased grid-anode capacitance as, for example, if the anode is indented opposite the support members. Since electron transit time increases as the square of frequency, an increase in electrode spacing limits the frequency of operation. Excessive grid -anode capacitance, on the other hand, critically affects high frequency operation for two reasons. First, the gain-bandwidth product for a high frequency amplifier=g /21|-C where g is mutual conductance, and where C is the output capacitance, primarily grid-anode capacitance. In order to attain satisfactory high frequency operation not only must the mutual conductance, g be large but also the output capacitance must be small. Secondly, the output capacitance must be small because the voltage present in the anode circuit'is quite high; it is much higher than the input voltage across grid and cathode for example. A large output capacitance produces an excessive grid-anode charging current and consequently contributes to grid overheating. Proximitybetween grid and anode structures is also restricted, on account of the high voltage present therebetween, to a spacing which will not cause high voltage breakdown. Effective location of a fine grid and support structure between the cathode and anode of a high power, high frequency electron discharge device therefore suffers from severe restrictions and limitations particularly as they affect the discharge devices successful operation.

It is accordingly an object of the present invention to overcome the foregoing disadvantages in providing an improved high power electron discharge device structure, operating at high current densities and at high frequencies, the device having a low output capacitance with high mutual conductance. According to a preferred embodiment of the present invention, a miniature, high-power, high frequency electron discharge device comprises planar cathode and anode electrodes and a grid electrode therebetween having its nearest fine conductor portions positioned very close to the cathode. The grid electrode comprises a comparatively heavy metal frame including a circumferential metal ring with a plurality of relatively massive bars extending thereacrosssupporting fine grid conductors on the anode side of the bars. The cathode electrode surface is recessed to receive these support bars in channels or indentations provided therein, with a major portion of the bars actually extending considerably below the cathode emitting surface. The bars provide solid support and a cooling function while intercepting substantially no current emitted from the cathode since the bars are substantially below the emitting surface thereof.

A typical discharge device according to the present invention includes a first set of grid wire conductors extending in a direction transverse to the support bars on the anode side thereof, While a multiplicity of finer conductors are located between the first conductors and the support bars. The finer conductors run transverse to the first conductors on the cathode side thereof, thus completing a grid mesh configuration. The bars substantially eliminate any movement of the grid conductors even though the fine grid conductors are positioned close to the cathode and the cathode is heated to provide on the order of one ampere or more emission per sqnarecentimeter of cathode area. Current and heat are conducted from the fine conductors to the circumferential ringin afirst direction via the support bars and in an orthogonal Y direction via the heavier grid conductors extending be- The cooling and support attained makes possible close placement of the fine thin grid conductors relative to the cathode. The fine grid structure then provides a very high mutual conductance, and a very low output capacitance between grid and anode. Since the fine grid conductors are very close to the cathode (on the order of one mil), the grid-cathode or input capacitance is not materially changed by the aforementioned placement of the support bars below the surface of the cathode because the bars are not nearly as close to a cathode surface as the fine grid conductors. Therefore the area of the bar surface is an unimportant factor. Moreover, very slight increases in input capacitance are more readily tolerated than an increase in output capacitance inasmuch as the grid-cathode input voltage is relatively low, especially in a high mutual conductance tube, and draws a very low input charging current, whereas the voltage between anode and grid is comparatively high. The fine grid construction also makes possible a substantially uniform anode field across the cathode, preventing spotty cathode erosion and failure at the high power levels employed. The discharge device according to the present invention produces power outputs in excess of one kilowatt at efficiencies above 60% at the frequencies of interest.

The subject matter which I regard as my invention is particularly pointed out and distinctly claimed in the concluding portion of this specification. The invention, however, both as to organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings wherein like reference characters refer to like elements and in which:

FIG. 1 is an elevational view, partially in section, of a high frequency, high power electron discharge device according to the present invention,

FIG. 2 is a perspective view, partially cut away, illustrating features of the principal electrodes of the electron discharge device in accordance with the present invention,

FIG. 3 illustrates a step in the manufacture of a grid electrode according to the present invention,

FIG. 4 illustrates another step in the manufacture of a grid electrode in accordance with the present invention,

FIG. 5 illustrates still another step in the manufacture of the aforementioned grid electrode,

FIG. 6 is a view of a grid frame employed in accordance with the present invention,

FIG. 7 illustrates a foil ring for brazing together portions of the aforementioned grid electrode,

FIG. 8 illustrates another step in manufacturing the aforementioned grid electrode,

FIG. 9 is a perspective view of a portion of a grid electrode in accordance with a second embodiment of the invention,

FIG. 10 illustrates a step in the manufacture of a grid in accordance with said second embodiment,

FIG. 11 is an exploded view illustrative of a double grid construction in accordance with the present invention,

FIG. 12 is a first cross-section of such double grid construction,

FIG. 13 is another cross-section of the double grid construction having excess insulating material removed,

FIG. 14 illustrates a step in the formation of the double grid embodiment, and

FIG. 15 illustrates another step in the manufacture of the double grid embodiment.

Referrings to FIGS. 1 and 2, a high power, high frequency electron discharge device embodying the present invention includes a stud-shaped anode 1 having a circular planar surface; a cathode 2 having an active surface generally conforming to and spaced from that of the anode, the active surface of the cathode having raised planar emitting portions 3 coated with appropriate electron-emit ting material; and a grid electrode 4 interposed between the anode and the cathode emitting surface. The aforementioned electrodes are quite small in diameter, approximately on the order of one inch or less, in order to reduce inter-electrode capacitance and thereby facilitate high frequency operation of the tube. High power output operation is then secured in accordance with the present invention by means of unusually high emission current density, preferably one ampere per square centimeter or more. The cathode, 2, is conveniently heated to a high temperature by a bonded heater element 5 of the type set forth and claimed in the copending application of August I. Kling for Heated Cathode and Method of Manufacture, Ser. No. 247,171 now abandoned, filed Dec. 26, 1962, and assigned to the assignee of the present invention. Connec tion 6 joins the aforementioned heater element 5 to terminal 7 while a thin cylindrical cathode support 8, desirably formed of hafnium, completes the circuit between heater element 5 and terminal member 9.

The outer portion of envelope of the tube is formed of ceramic insulating cylindrical members bonded to metal cylindrical terminal members. The ceramic insulating members are desirably fosterite because of its low dielectric constant. The metal connecting terminals and internal elements such an the tu'bes anode and cathode are desirably titaium, a low emission material exhibiting continuous gettering properties during high power operation. Ceramic insulating cylindrical member 10 separates grid terminal ring 11 from heater terminal 9 and at the same time carries grid support 12. The grid terminal ring 11 includes a depending flange 13 connecting the terminal ring with grid support 12, and is also used for centering the latter within the vacuum enclosure. A ceramic cylinder 14 in turn separates grid terminal ring 11 from anode terminal ring 15. An extension 16 of this anode ring is apertured to receive anode 1 which it positions at a distance of approximately 10 to 30 mils from the emitting surface 3 of the cathode. The anode is additionally provided with a radiator stud 17 for conducting heat away from the anode. In an exemplary device constructed in accordance with the embodiment of FIGS. 1 and 2, the overall envelope was approximately 1 inch in diameter by 1% inches in length.

From the standpoint of high frequency operation in the range of one gigacycle per second and higher, it is desirable to include the fine conductor thin grid in close spaced relation to the cathode electrode. Such a grid contributes toward a more uniform electric field pattern from the anode as seen at the active surface of the cathode electrode, thereby deterring tube breakdown and erosion of the cathode emitting surface. Moreover a fine grid positioned close to the cathode is advantageous from the point of view of grid control and transit time. Such a grid should have a conductor spacing comparable to its distance from the cathode emitting surface in order to achieve adequate electron control. Unfortunately, conventional fine conductor grids have not been capable of withstanding the high temperatures and large currents involved in very high frequency, high power output operation in a tube with small diameter electrodes. For example, the cathode of the illustrated embodiment operates at about 850 C. in order to furnish a current density of between one and two amperes per square centimeter. Furthermore R.F. displacement currents flowing into and out of the grid-cathode and grid-anode capacitances at high frequencies are themselves sufficient to melt a fine conductor grid. Under these conditions the usual fine grid is unstable in its position and warps axially towards the cathode or the anode.

In accordance with a feature of the present invention, a fine conductor grid structure is provided, which structure includes a plurality of relatively massive grid support bars 18, illustrated in FIGS. 1 and 2. These relatively massive metal grid bars, which are preferably parallel and materially thicker in the grid-cathode direction than the fine grid conductors, carry current to and from the fine grid conductors and heat away from the fine grid conductors. They also securely position the fine grid conductors at its correct axial location close to the cathode and prevent any movement or warping thereof. The bars extend from one side to the other of a relatively massive circumferential support frame or ring 19 and are preferably integral therewith. Frame 19 is in turn secured to cylindrical grid support 12. According to an important feature of the invention, the surface of the cathode electrode is recessed to provide a plurality of channels 50 for receiving the support bars 18 in spaced relation to the side walls and dwells of the channels 50, with a major portion of the bars 18 actually extending below the cathode emitting surface. The grid support bars are adequately accommodated substantially entirely on the cathode side of the grid without increasing the interelectrode spacing in the tube, and without substantially increasing interelectrode capacitance. The walls of channels 50 are spaced from bars 18 at a distance appreciably greater than the close spacing between the cathode emitting surface and the surface of the active grid. Therefore only a negligible increase in grid-cathode capacitance is attributable to the presence of the bars 18. Moreover, since nothing is interposed between the flat, small diameter anode surface and the upper surface of grid 4, the gridanode capacitance can be quite small; therefore little charging current flows therein, while the small capacitance also contributes to a high bandwidth factor.

Furthermore, the devices high voltage rating is not compromised inasmuch as nothing is interposed between the anode and the fine conductor grid. Because the dwells of the channels 50 are free of electron-emissive coating the grid support bars themselves do not intercept any substantial emission of electrons from the cathode emitting portion 3, but rather substantially all such emission passes through the fine grid conductor areas. A substantially uniform anode field reaches the cathodes emitting portions through the fine grid conductors, thereby deterring breakdown attributable to cathode hot spots and the like.

In the embodiment illustrated in FIGS. 1 and 2, distances are not shown exactly to scale but rather the electrode illustration is expanded somewhat for ease of understanding. In discharge devices constructed in accordance with the present invention, the dimensions and spacings involved are desirably quite small. The spacing between the emitting surfaces 3 of the cathode and the fine conductor grid is usually on the order of only 1 to 3 mils, while the spacing between the grid and theanode is approximately from to 30 mils, 20 mils being representa tive. The bars 18 are relatively massive as compared with the much smaller grid conductors described hereinbelow and are appropriately rectangular in cross-section. In one exemplary device these bars were approximately 0.03 3

inch in vertical thickness by approximately 0.008 inch in width. The frame 19 may have the same thickness but has a cross-sectional width about four or five times that of the bars. The frame and bars are preferably integral, with the bars 18 extending across the frame 19 at the same level as the frame. The bars 18 are typically spaced 5 to 6 mils from the sides of recessed channels 50, which channels are also appropriately rectangular in crosssection, 10 to 12 mils being a typical spacing between the bars lower edges and the dwells of the cathode channels. In one exemplary construction in accordance with the present invention, the fine grid includes first conductors 20 having a diameter on the order of the spacing between the grid and the cathode (e.g. 1 to 3 mils), which first conductors extend across the frame 19 and bars 18 in a direction transverse to bars 18. Finer conductors 21 are materially smaller in diameter than the spacing between the grid and the cathode emitting surface, but have a close spacing therebetween on the order of the gridcathode spacing. Typically these conductors are on the order of 0.0003 inch in diameter and are located between the order of one gigacycle with bars 18 and conductors 20. A large multiplicity of these fine wires 21extend in a direction transverse to conductors 20 preferably perpendicular thereto from one side of frame 19 to the other, and are therefore substantially parallel to relatively massive grid support bars 18. This orientation of fine grid conductors 20 and 21 is advantageous since the fine conductors 21 have only a very short span between conductors 20. The larger conductors 20 similarly span only the distance from one bar 18 to the next. The bars 18 and the first conductors 20 therefore conduct heat and current in orthogonal directions allow ing the extremely fine conductors 21 to be closely spaced from the cathode emitting surfaces without deleterious effects either because of direct heating or because of large displacement currents or the like flowing in the fine grid conductors. The finer conductors 21 are preferably secured between conductors 20 and bars 18 because in this manner their position is closest to the cathode (e.g. the 1 to 3 mil spacing) for attaining maximum grid control.

The grid conductors 20 and 21 are brazed or soldered to one another forming a mesh, and are brazed or soldered as well to bars 18 and frame 19. Wires 21 are preferably tungsten, while the coarser wires 20 are gold-plated tungsten, molybdenum or a tungsten-molybdenum alloy. The integral frame 19 with bars 18 is preferably tungsten, although molybdenum and tungsten-molybdenum alloys are also suitable. The foregoing materials allow electrode degassing at between 1200 and 1600 C., tube degassing at 1000 C. and subsequent cathode operation at approximately 850 C. to supply between one and two amps per square centimeter grid emission.

The cooling and support attained with the foregoing structure makes possible the placement of the fine grid conductors at the indicated extremely close spacing to the high temperature, high current density cathode, the finer grid conductors conducting current, and heat, for only relatively short spans between the heavier conductors. The multiplicity of close-spaced fine grid conductors, positioned very close to the cathode, are then available for exerting a high degree of control on the electron current flowing from the cathode to the fiat juxtaposed anode. Electron transit time is minimized because of the close spacing of the grid relative to the cathode and because of the small diameter of the grid conductors, thereby facilitating high frequency operation. The fine grid structure according to the present invention including fine grid conductors spaced, for example, approximately 1 /2 mils from the cathode surface and from each other, provides a mutual conductance, g of 300,000 micromhos, or about five times that heretofore available. With a gridanode spacing of approximately 20 mils (there being no support structure therebetween), the output capacitance between grid and anode ranges between 3 and 6 picofarads, 4 picofaradsbeing a typical value. Since amplifier bandwidth is a function of mutual conductance and output capacitance according to the experession, bandwidth=g /21rC the tube according to the present invention is very useful at high frequencies.

The construction of the tube according to the present invention and especially the grid structure thereof easily withstands high levels of dissipation. Therefore an appreciable increase in power output at high frequencies is accomplished in the miniature tube. Discharge devices according to the present invention can provide a continuous wave output of one kilowatt at frequencies on an anode voltage of 2000 volts. Because of the devices large mutual conductance and high anode current, high power gains are also possible in the indicated high frequency range. For example, with the mutual conductance of 300,000 and anode current density of 1 /2 amperes per square centimeter, the tube in the specific example provides a power gain of 20 at a frequency of one gigacycle. A kilowatt of output is produced with 50 watts of grid drive in a grounded-grid circuit configuration wherein an efiiciency of approximately 70% is attained. At slightly lower power levels and at slightly lower frequencies, higher efficiencies above 80% and power gains up to 100 have been achieved.

The manufacture of the fine structured, high dissipation control grid is illustrated in FIGS. 38. First a metal mandrel 22, indented on either side thereof, is provided in its indented areas with inserts 23 and 24 of refractory insulating material, boron nitride being suitable. The mandrel is secured in chuck jaws 25 and 26 of a lathe or similar device for imparting a rotational motion 27 to the mandrel. As the mandrel is rotated, wire 20 is wound on the mandrel 22 from the spool 28 arranged to travel along the mandrel via leadscrew 29 in order to provide approximately 80 turns per inch across the boron nitride inserts 23 and 24. The wire 20, corresponding to reference numeral 20 in FIG. 2, is conveniently 0.0019 inch diameter gold plated tungsten wire. The wire is gold plated for brazing purposes, as hereinafter described. After the mandrel is wound in one direction across the boron nitride inserts 23 and 24, the mandrel is turned 90 and a finer tungsten wire 21 is wound in a direction substantially perpendicularly across the wire 20 as shown in FIG. 4. The second and finer wire is conveniently 0.003 inch diameter tungsten wire and is wound at about 700 turns to the inch.

The mandrel is now removed from the lathe and placed between two boron nitride plates 30 and 31 as illustrated in FIG. 5, and heat and pressure are applied therebetween for brazing of the heavier and finer wires at their crossover points. Gold is used as the wire coating and brazing material because of its low vapor pressure within the finished tube. The wire mesh thus formed on each side of the mandrel is held between the boron nitride plates 30 and 31 and the boron nitride plates 23 and 24, respectively, while the brazing is accomplished. The fine grid structure is then ready for attachment to frame 19 illustrated in FIG. 6, frame 19 being provided with support bars 18 extending thereacross. As hereinbefore stated, this bar and frame structure is preferably unitary and formed of molybdenum, tungsten or alloys thereof. Referring to FIG. 8, two grid elements are conveniently formed at the same time, one on each side of the mandrel. A first frame 19 and a second frame 19a are disposed one on either side of the mandrel in a position coincident with the boron nitride inserts. The frames 19 and 19a are positioned such that their bars 19 are substantially parallel with fine conductor wire 21. Gold foil ring 32, illustrated in FIG. 7, is placed between each frame and the mesh grid structure. Then boron nitride plates 34 and 35 are placed on either side of frames 19 and 19a and while pressure is exerted therebetween the combination is brought to a temperature sufficient for brazing the frames 19 and 19a to the wire mesh with the intervening gold foil material, 32.

In accordance with another embodiment of the present invention, a finely perforate thin grid structure is formed partially employing a fine perforate etched member, one of which is illustrated in FIG. 9. In this embodiment, a very thin etched member includes a ring portion 19', bar or rib portions 18' extending thereacross and first conductor portions 20' extending across the ring between ribs 18'. In this embodiment of the invention, one such etched member is formed to have an identical configuration as the frame and bar member of FIG. 6 with which it will be cooperatively employed. Thus such an etched member as illustrated in FIG. 9 is later brazed with similar portions in registry with the frame and bar structure of FIG. 6, leaving only the finer cross conductors yet to be provided. The finely perforate etched member of FIG. 9 itself may be formed in accordance with the method described and claimed in copending application of August I. Kling and James E. Beggs, Ser. No. 334,306, filed Dec. 30, 1963, and assigned to the assignee of the present invention. This etched member is conveniently composed of tungsten or molybdenum and is gold plated for brazing purposes. The finer conductor is added to etched member 40 as illustrated in FIG. 10. In FIG. 10 a mandrel 36 indented to receive one or more boron nitride inserts 37 is rotated in chuck jaws 38 and 39. One or more etched members 40 are placed upon the boron nitride inserts 37 with their ribs 18' oriented in the turning direction while 0.0003 inch tungsten wire 21 is wound around the mandrel at about 700 turns to the inch. After one or more etched members are wound over, the wire and the etched members are secured one to the other with heat and pressure in the manner illustrated in FIG. 5. Then an etched member is aligned with a frame such as illustrated in FIG. 6, with a gold foil ring 32 as shown in FIG. 7 disposed therebetween, and the two are secured by heat and pressure. In this manner, an electrode is conveniently formed since it is only necessary to wind one fine conductor in one direction around the mandrel. According to the present state of the art, fine conductor 21 is preferably a fine wire as indicated inasmuch as etching to this degree of fineness is relatively unreliable.

In accordance with another embodiment of the present invention, a multiple fine grid structure is provided which may be employable as a control grid and screen grid. The first step in the formation of such double grid is illustrated in FIG. 11 wherein a first gold-plated etched grid member 41, similar to etched grid member 40 of FIG. 9, is aligned with a similar gold-plated etched grid member 42 separated therefrom by a thin sheet of very refractory insulating material 43. An excellent refractory insulating material for this purpose is boron nitride. Although the three layers are shown apart in FIG. 11 for purposes of improved illustration, the layers are actually laminated together as shown in the FIG. 12 cross-section. The etched members 41 and 42 are bonded to the intervening boron nitride. Then the boron nitride is removed from the aperture areas as by application of a fine jet blast of air including abrasive material. The resulting cross-sectional structure is illustrated in FIG. 13.

To complete the double grid structure, a fine wire, e.g. 0.0003 inch diameter tungsten wire 46, is wound around mandrel 44 in FIG. 14, mandrel 44 including an indented boron nitride insert 45. Then, as illustrated in FIG. 15, the laminated structure of FIG. 13 is secured temporarily, as by gluing, to the top of the wire 46 wound on the boron nitride insert, with ribs 18' oriented in the same direction as fine wire 46. Then a second similar fine wire 47 is wound across the top of etched grid member 41. In this manner fine grid conductors are easily provided across both etched members of the laminated double grid. The laminated grid members and the fine wire conductors are then brazed together employing heat and pressure in the manner of FIG. 5. Then a relatively massive frame and bar member of the FIG. 6 type is aligned with and secured to the fine grid structure employing heat and pressure as in FIG. 8. The double grid is then placed in an electron discharge device of the FIG. 1 type wherein the lower of the two etched grids may function as a control grid and wherein the remaining grid structure is conveniently utilized as a screen grid. It is understood an additional connecting ring terminal (not shown) would be employed to secure electrical connection to the screen grid. Although a two-grid combination is illustrated in FIGS. 11-15, it is understood the same procedure is usable to secure a larger suitable number of grids.

In summary, the present invention provides a high power, high frequency electron device which is relatively small in size, being typically on the order of one inch in diameter. The reduced size of its planar electrodes reduces inter-electrode capacitance and renders it more suitable for high frequency operation. High power operation is then secured employing high cathode emission density. The emission density is approximately an ampere per square centimeter or greater, and is about five to ten times the to 200 milliampere per square centimeter commonly employed heretofore. Control of the high emission density currents is facilitated or made possible ac cording to the present discharge devices construction including a high dissipation grid structure closely positionable to the high temperature, high emission density cathode. As a result of the close spacing from the cathode, transit time is reduced thus enhancinghigh frequency operation while this factor together with the close spacing between a multiplicity of fine grid conductors produces an extraordinarily high mutual conductance. These advantages are attained according to the present invention Without undue interference with the anode field as seen at the cathode, thus rendering the tube advantageously unsusceptible to arc breakdown and quite suitable for high power operation. The active part of the tubes grid structure comprises a mesh of fine conductors super-imposed upon support bars residing on the cathode side of the fine grid mesh, a major portion of the support bars being accommodated in recessed channels in the cathode. These bars do not interfere with tube operation or electrode spacing and cause no capacity problem between electrodes inasmuch as the electronically effective portion of the grid is spaced much closer to the cathode surface than are these bars. The construction provides for the heat dissipation and current carrying requirements of the grid structure. Solid support is attained, preventing axial movement of the fine grid conductors under the high temperature and high current conditions.

While I have shown and described several embodiments of my invention, it will be apparent to those skilled in the art that many changes and modifications may be made without departing from my invention in its broader aspects; and I therefore intend the appended claims to cover all such changes and modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A high power output electron discharge device for use at high frequencies comprising an anode electrode, a cathode electrode provided with recesses extending below its surface, a grid structure including grid conductors closely spaced to said cathode between said anode and cathode, and conductive support members joined to said grid conductors having a' greater thickness in the anodecathode direction than said grid conductors, wherein said support members are spaceably received in said recessesin said cathode at least partially below the surface of said cathode for conducting heat and current to and from said grid conductors while maintaining the said grid conductor spacing relative to said cathode.

2. A high power output electron discharge device for use at high frequencies comprising a planar :anode electrode and a spaced cathode electrode provided with a plurality of channel shaped recesses, a fine planar grid electrode located closely adjacent said cathode between said cathode and said anode electrode with a substantially uniform spacing between said grid and anode electrodes, and support members for said grid electrode, which support members are received in said recesses of said cathode electrode for maintaining close spacing between said cathode and grid electrodes and for maintaining said uniform spacing between said grid and anode electrodes.

3. A high power output electron discharge device for use at high frequencies comprising spaced planar anode and cathode electrodes, the said cathode electrode ebing provided with a plurality of recessed channels and having a flat emitting surface therebetween providing an emission current density on the order of one ampere per square centimeter, a fine planar grid located closely adjacent the emitting surface of said cathode, support bars for said grid located on the cathode side of said grid with a major portion of said bars received in said recessed channels of said cathode below said cathode emitting surface, wherein the spacing between the channel surfaces and said bars is greater than the spacing between said :athode surface and said grid.

4. A high power output electron discharge device for operation at high frequencies comprising a planar anode electrode, and a cathode electrode spaced therefrom and provided with a plurality of substantially parallel recessed channels, said cathode having a planar forward emitting surface located between said channels, a plurality of support bars spaceably received in said channels with a major portion of said support bars indented therein and with the top surfaces of said support bars disposed substantially in a common plane just above the plane of said emitting surface, a fine conductive grid electrode secured across the top of said support bars on the anode side of said support bars, a circumferential support frame joining the ends of said support bars, and insulating means for positioning said circumferential support frame to locate said fine grid electrode just above the plane of said cathode emitting surface in close spaced relation thereto. 7 p

5. A high power output electron discharge device for operation at high frequencies comprising a planar anode electrode and a cathode electrode spaced therefrom provided with a plurality of substantially parallel recessed channels and having a planar forward emitting surface located between said channels, a plurality of support bars spaceably received in said channels with a major portion of said support bars indented therein and with the top surfaces of said support bars disposed in a common plane just above the plane of said emitting surface, a fine mesh grid electrode positioned across the top of said support bars substantially on the anode side of said support bars including first conductors finer than said support bars extending thereacross in a first direction, and second conductors finer than said support bars extending thereacross in a second direction, and a circumferential support frame joined in common to both ends of said support bars.

6. A high power output electron discharge device for operation at high frequencies comprising a planar anode electrode, and a cathode electrode in spaced relation thereto having a forward emitting surface producing electron emission in excess of one ampere per square centimeter of emitting area, a circumferential support ring at least a portion of which is substantially coincident with a plane between said anode electrode and said cathode electrode, said support frame further including massive substantially parallel rectangular grid support bars extending thereacross in a common direction from one side of said ring to the other, said cathode electrode being provided with recessed channels spaceably receiving said massive grid support bars with a major portion of said grid support bars extending below emitting surface of said cathode, a fine mesh grid electrode disposed across said support bars on the anode side thereof in close spaced relation to said cathode emitting surface including first conductors transverse to said bars and finer conductors transverse to said first conductors so that heat and current may be carried by the finer conductors to the said first conductors and by said first conductors to said massive support bars to maintain said conductors at a temperature near the temperature of said support ring.

7. A high power output electron discharge device for operation at high frequencies comprising spaced circular anode and cathode electrodes, wherein said anode electrode has a planar surface facing said cathode, and said cathode electrode is provided with a plurality of recessed channels and a planar emitting surface therebetween facing said anode, a circumferential support ring located generally between said cathode and anode, said circumferential support ring integrally including massive support bars extending across said ring and spaceably received within said recessed channels of said cathode electrode, said support bars having top surfaces located in a common plane a very small distance above the emitting surface of said cathode electrode, a multiplicity of first conductors disposed across said bars from one side of said ring to the other and physically joined to said ring and said bars, a multiplicity of fine second conductors disposed across said first conductors and bonded between said first conductors and said bars, said fine second conductors having a diameter substantially less than the spacing between said second conductors and the emitting surface of said cathode electrode, and cylindrical enclosure means for insulatably supporting said circumferential frame and positioning said fine second conductors closely adjacent said cathode electrode at a distance on the order of a mil therefrom.

8. A high power output electron discharge device for operation at high frequencies comprising a planar anode electrode and a cathode electrode spaced therefrom provided with a plurality of substantially parallel recessed channels and having a planar forward emitting surface located between said channels, a plurality of support bars spaceably received in said channels with a major portion of said support bars indented therein and with the top surface of said support bars disposed in a plane just above the plane of said emitting surface, a fine mesh grid positioned across the top of said support bars including a thin reticulated structure having first ribs extending in a first direction in substantial registry with said support bars and finer second ribs extending in a second direction between said first ribs, and fine conductors disposed in a plane between said support bars and said reticulated structure, said fine conductors extending between said second ribs and having a smaller cross-section than said ribs, said fine conductors being joined to said ribs and said support bars.

9. A high power output electron discharge device for operation at high frequencies comprising: a planar anode electrode and a cathode electrode spaced therefrom provided with a plurality of substantially parallel recessed channels and having a planar forward emitting surface located between said channels; a plurality of support bars spaceably received in said channels with a major portion of said support bars indented therein and with the top surface of said support bars disposed in a plane just above the plane of said emitting surface; and a fine mesh grid electrode positioned across the top of said support bars including a first metallic reticulated structure with first ribs extending in a first direction in substantial registry with said support bars, second ribs extending therebetween, and fine conductors disposed across said second ribs; a second reticulated structure having ribs in registry with the ribs of said first reticulated structure; and an insulating layer between said first and second reticulated structures having first and second ribs in substantial registry with the ribs of said reticulated structures for electrically insulating said first and second reticulated structures.

10. For use in an electron discharge device which includes an anode and a cathode, a grid structure comprising a conductive circumferential ring, a plurality of conductive support bars connected to said ring and extend ing in a first direction, a plurality of first conductors finer than said support bars connected to said ring and extending across said support bars in a second direction, and a plurality of second conductors finer than said first conductor-s connected to said ring and extending in a direction across said first conductors and located in between said support bars and said first conductors, said ring and bars having .a large cross section relative to said conductors and providing support and cooling for both said first and second conductors.

11. For use in an electron discharge device including an anode and a cathode, a grid structure comprising a conductive circumferential ring, a plurality of conductive support bars connected to said ring and extending in a first direction, a plurality of first conductors connected to said rings and extending across said support bars in a second direction, and a plurality of second conductors finer than said first conductors connected to said ring and extending in a direction across said first conductors and located in between said support bars and said first conductors, said bars and said ring having a large cross section relative to said conductors and providing support and cooling for both said first and second conductors, said discharge devices cathode including channels for spaceably receiving said support bars between an emitting surface closely adjacent said second conductors of said grid structure.

References Cited UNITED STATES PATENTS 2,261,154 11/1941 Hansen et al. 313-348 2,296,885 9/1942 Vance 31.3-348 2,461,303 2/1949 Watson 313-265 2,678,486 5/1954 Chick et a1 313-348 X 2,717,974 9/1955 Wihtol 313-348 JOHN W. HUCKERT, Primary Examiner. A. JAMES, Assistant Examiner. 

1. A HIGH POWER OUTPUT ELECTRON DISCHARGE DEVICE FOR USE AT HIGH FREQUENCIES COMPRISING AN ANODE ELECTRODE, A CATHODE ELECTRODE PROVIDED WITH RECESSES EXTENDING BELOW ITS SURFACE, A GRID STRUCTURE INCLUDING GRID CONDUCTORS CLOSELY SPACED TO SAID CATHODE BETWEEN SAID ANODE AND CATHODE, AND CONDUCTIVE SUPPORT MEMBERS JOINED TO SAID GRID CONDUCTORS HAVING A GREATER THICKNESS IN THE ANODECATHODE DIRECTION THAN SAID GRID CONDUCTORS, WHEREIN SAID 